The Collaborative International Dictionary of English v.0.48:

Opercle \O"per*cle\, n. [Cf. F. opercule. See Operculum.]
   1. (Anat.) Any one of the bony plates which support the gill
      covers of fishes; an opercular bone.
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   2. (Zool.) An operculum.
      [1913 Webster]